1. Field of the Invention
This invention relates to a multilayer organochlorine-free tubular casing consisting of
a. as a regenerated cellulose substrate, PA1 b. optionally a layer of primer, PA1 c. a 5 to 40 .mu.m thick, organochlorine-free polymeric water vapor barrier layer which is characterized in that it has a permeability to water vapor of at most 50 g/m.sup.2.24 h and a surface tension of.ltoreq.34 mN/m, PA1 d. a 5 to 40 .mu.m thick, polymeric organochlorine-free oxygen barrier layer, characterized in that it has a permeability to oxygen of at most 120 cm.sup.3 /m.sup.2.24 h bar and a surface tension of.gtoreq.38 N/m, PA1 a. a regenerated cellulose substrate, PA1 b. optionally a layer of primer, PA1 c. a 5 to 40 .mu.m thick, organochlorine-free oxygen and water vapor barrier layer which has a permeability to water vapor of at most 50 g/m.sup.2.24 h and a surface tension.ltoreq.34 mN/m and PA1 d. a 5 to 40 .mu.m thick, chlorine-free oxygen barrier layer which has a permeability to oxygen of at most 120 cm.sup.3 /m.sup.2.24 h bar and a surface tension of.gtoreq.38 N/m. PA1 the coating should show adequate adhesion to the substrate and PA1 should undergo shrinkage to the same extent as the substrate. PA1 In addition, these properties should be retained despite the thermal and mechanical stressing typically encountered in sausage production and distribution (cf. G. Effenberger, Wursthullen Kunstdarm, Herstellung, Eigenschaften und Anwendung, Holzmann Buchverlag, D-8939 Bad Worishofen (1991)).
to a process for its production and to its use as a casing for sausages of the Bruhwurst and Kochwurst type (fine emulsion sausage and cooked sausage).
In the context of the invention, an "organochlorine-free tubular casing" is understood to be a casing free from covalently bonded chlorine atoms.
2. Description of Related Art
Tubular casings based on cellulose, for example regenerated cellulose, which are produced by longitudinally folding and bonding the overlapping, longitudinally extending margins, are already known (see, for example, EP 0 037 543, EP 0 054 162, U.S. Pat. No. 2,148,884, U.S. Pat. No. 2,226,442, U.S. Pat. No. 2,685,769, U.S. Pat. No. 2,685,770, U.S. Pat. No. 2,757,495 and U.S. Pat. No. 2,773,773).
Other processes for the continuous production of fiber-reinforced cellulose hydrate casings and machines for carrying out these processes are described in DE 2 829 102 and DE 2 512 994.
Tubular casings of the type in question are permeable inter alia to water vapor and oxygen which is desirable, for example, where they are used as casings for sausages of the Rohwurst (dry sausauge) type, but is a disadvantage where the casings are used for sausages of the Kochwurst and Bruhwurst type. Sausages of this type require casings that are impermeable to water vapor in order to avoid losses of water during the production and storage of the sausage. They also require an effective oxygen barrier to prevent oxidative damage to the sausage mix.
Accordingly, tubular cellulose casings are often subsequently coated to achieve these barrier layer properties. In addition to the barrier effect, suitable coatings must also show adequate adhesion to the tubular casing and sufficient resistance to be able to withstand the various thermal and mechanical loads typically applied during the processing of sausages. In addition, the coated casing has to be able to undergo hydrophilic shrinkage during ripening of the sausage and must show adequate stability in storage.
For this reason, thermally stable, elastic, halogenated polyolefins, preferably polyolefins containing vinylidene chloride (PVDC) or copolymers thereof and copolymers of acrylic acid, methacrylic acid and acrylonitrile are used for this purpose (cf. for example DE 2 512 994 and EP 0 054 162).
For ecological reasons, however, there is a need to use organochlorine-free systems for this purpose.
Casings based on cellulose hydrate suitable for use as casings which have a coating of a vinylidene chloride homopolymer or copolymer, are commercially available either as rolls or as cuts tied at one end. Sausage casings in relatively large quantities, for example of 20 to 50 m or more, are generally gathered and compressed to form rod-like structures approximately 20 to 50 cm in length (strands).
The tubular casings are then continuously filled with sausage mix by known sausage filling machines which force the meat into the tube. However, this efficient sausage filling process cannot be carried out with casings of cellulose hydrate having a barrier layer coating based on thin, 5 to 40 .mu.m thick chlorine-free polymers or copolymers, because casings of this type are unable to withstand the severe mechanical stressing involved. The mechanical stressing damages the coating above all at the edges of the folds. This leads to an unwanted increase in the permeability of the coating to water vapor and oxygen, with the result that the keeping properties and quality of the sausage are permanently impaired.
Accordingly, the problem addressed by the present invention was to provide tubular casings of which the coating would be free from organochlorine and which, at the same time, would exhibit the properties required for the production of sausages of the Kochwurst and Bruhwurst type which have hitherto been provided by PVDC-containing coatings.
This problem has surprisingly been solved by providing the tubular casing with a multilayer, organochlorine-free polymeric coating having various surface tensions.
The solution to this problem as provided by the invention is surprising because it is known that the polymer coatings with surface tension of 36 to 45 mN/m, such as acrylonitrile copolymers etc., are hydrophilic plastics with a water absorption capacity of.gtoreq.2%. In addition, the combination of the various components of the present coating surprisingly provides distinctly better barrier properties than the sum total of the barrier effects of the individual components.
It is known from the literature that polyvinyl alcohols in the dry state are distinguished by excellent barrier behavior with respect to oxygen (cf. for example, Polymer Handbook, Chapt. VI, page 439, John Wiley and Sons, New York/Toronto/Brisbane, 1989).
These polymers are also highly hydrophilic plastics. They have a water absorption capacity of.gtoreq.2% and their favorable oxygen barrier property is adversely affected by the water taken up. For this reason, they cannot be used in the field in question.